1. Field of the Invention
The present invention relates to the creation, replacement, restoration and reinforcement of concrete structure connections.
2. Description of Related Art
Precast, prestressed concrete parking garages have become one of the most popular methods for parking garage construction. This construction consists of fabrication of discrete precast concrete elements or members that are transported to the construction site, lifted into position and connected together.
As shown in the prior art drawings of FIGS. 1 and 2, precast concrete structures typically consist of “tee” or “double tee” beams 26, girders 34, columns 32 and lateral bracing members 30. A lateral bracing member 30 may be a shear wall, brace or frame. The tee/double tee beams are connected together to form the floor/deck. The deck supports gravity loads from vehicles and may be formed from one or more diaphragms. Diaphragms are, in effect, large horizontal beams that transmit lateral loads from seismic and wind events to points of lateral support, typically lateral bracing members 30. The diaphragm may be composed of one or more rows of precast concrete members 26. To form the deck the tee beams are connected to one another with two types of connections, shear connections and chord connections. Tension, compression, vertical shear and horizontal shear are each addressed with connections to resist the respective force or load. Shear connections 56 provide mutual support to gravity (wheel) loads while also transmitting shear within the plane of the deck. Chord connections 58 provide mutual support to gravity (wheel) loads and form chords that restrain tension and compression forces due to in-plane bending of the diaphragm in the manner similar to that in which reinforcement steel restrains tension in a concrete beam under bending. FIG. 2 shows chords 45 extending from one end of the diaphragm to the opposite end.
An example of the precast member 26 is a double tee beam shown in FIG. 3 and includes a platform having a length L and a width W. The platform consists of a horizontal center panel 40 and flanges 24 extending outward from the center panel. The double tee beam 26′ includes a pair of beam webs 12 extending normal to and below the platform, the beam web having beam web ends 44 and beam web sides 46 extending between the beam web ends 44. The flange 24 includes flange ends 38 substantially parallel to the beam web 12.
Chord connections 58 are typically used in precast concrete structures and are shown in FIGS. 4A-4C and FIG. 5 while shear connections 56 may encompass the connections shown in FIGS. 4A-5 and provide stability from shear forces. Both shear connections and chord connections are typically achieved by placing a loose erection plate 22′, flat plate 76 or erection bar 22 between adjacent flanges 24 and welding them to steel plates 20, 20′ embedded within the precast members. Embedded steel plates 20, 20′ are installed during fabrication of the concrete member prior to placement of the concrete in the formwork. Anchorage of the plate within the concrete is typically achieved by welding the plate to a steel bar, stud or rebar 28 prior to fabrication. Weld joints 19 are made at the upper contact points of the embedded plates 20 and the bar 22 or plate 22′. Weld 76 is located at the upper contact point of the embedded plate 20 and the flat plate 76. The steel plates are positioned within the end of the flange 24 such that the face of each plate is exposed on the end of the flange. Once the tee beam is placed into position during fabrication of the concrete structure, the gap between embedded plates 20 are bridged with a dowel 22, loose erection bar 22′ or flat plate 76 and welded together. Once welded, this creates a continuous steel chord or shear connection 56 within the edge of the diaphragm/deck. The chord connections 58 have an upper cavity 90 which may be filled with a sealant and/or grout. Alternatively or in combination, a layer of concrete may be spread across the top of the flange 24 and flange connection. The shear connections 56 may also have an upper cavity 90 which may be filled with a sealant and/or grout. The chord connections 58 form chords 45 which are embedded in the platform of the diaphragm. The steel bar 28, the steel plate 20 and the erection bar 22′, flat plate 76 or plate 22 make up the chord 45 and typically extends through all of the platforms in the diaphragm.
The shear connection shown in the top plan view of FIG. 4D is a proprietary Vector Connector 41 consisting of a bent plate 25b with wings 25a embedded in the flange 24, and although it is not attached to rebar, the wings 25a provide sufficient anchorage to act as a shear connection. The bent plate 25b is welded to the bent plate of the adjacent Vector Connector 41 using an erection plate 22′. The Vector Connector is not sufficient for tension forces and usually supplements the welded chord connections. The Vector Connections are usually spaced between the chord connections 58 which are along or near the outer edges of the diaphragm.
One primary weakness of the systems shown in FIGS. 4A-4D is that the connection has insufficient geometry to resist the concrete members moving in a vertical direction in relation to each other causing the connector 22 to rotate about the weld joint or welded connection 19 since each welded connection 19 acts as a pivot.
FIGS. 5 and 6 show an embodiment of a prior art connector which includes a flat bar 76 welded to the embedded steel plates 20. This embodiment also has insufficient geometry to resist the concrete members moving in a vertical direction in relation to each other causing the connector 76 to rotate about the weld joint 47 or welded joint 49 since each welded joint 47,49 acts as a pivot. The flat bar 76 may rotate about each of the weld joints 47,49 when forces on the flanges 24 cause the flanges to move in a vertical direction in relation to one another. The movement of the flanges in this direction is also called translation.
The existing methods of construction produce numerous problems and failures, generally due to poor design, poor fabrication in the shop, poor construction in the field, and in service deterioration. Weld code provisions do not intend or allow welds to be used in the manner in which they are loaded in this connection.